Handsets used in the cellular communications industry benefit from optimum performance from antenna systems in order to maximize the two-way voice or data link between a remote base station and the handset. Most current cellphone antennas utilize either dipole, or half-dipole antennas, mounted external or internal to the handset, all of which may be susceptible to RF radio frequency loss to the hand and other inefficiencies related to their size and location on the handset.
Known wireless communications devices (WCD) utilize internally-mounted planar inverted “F” antennas (PIFA). Prior art PIFA's provide limited electrical performance over the current wide frequency ranges used in WCDs such as cellphones. One such band is the 1710-2170 MH range, which includes the 1800-1900 MHz and UMTS bands (world cellular and 3G bands). Prior art PIFA's have narrow bandwidth, omni- or near omni-radiation pattern, and relatively low efficiency. The omni-radiation pattern derives from the fact that the installation location of the PIFA resonator causes the ground traces of the printed circuit board (PCB) to be the primary radiating element of the antenna. Power loss to the hand and head of the handset user dramatically reduces antenna efficiency.
In a typical application, the link budget between a base station and a handset of the prior art is degraded by 6 dB within the high frequency range due to increased path loss, as compared to the 800-900 MHz bands. Cellphones typically operate at the same maximum power level in all frequency bands, low and high, and therefore an antenna system capable of recouping even a portion of the 6 dB loss would be highly desirable. Additionally, an antenna system that reduces power losses to the head and hand of the user is also highly desirable given the reduction of SAR.
FIGS. 15-17 depict top, end and side views of a prior art PIFA resonator 150 having top leg 152, side leg 153, an RF feed point leg 154, and a height dimension 155. FIGS. 18-19 depict top and side views of the PIFA resonator 150 as connected to a ground plane conductor 157 of a wireless communications device. Ground plane conductor 157 may be formed by the ground traces of a PCB of the WCD, such as a cellular handset. The resonator 150 is grounded to ground plane conductor 157 at location 158 which is at or very near the longitudinal edge 159 of the ground plane conductor 157. Additional aspects of PIFA antenna systems and wireless communications devices may be found in U.S. Pat. No. 7,230,574, entitled Oriented PIFA-type device and method of use for reducing RF interference, incorporated by reference herein.